The invention concerns a process for the splitting of water-soluble ethers. The invention also concerns a process for the production of 1,3-propanediol (PDO).
Generally ethers can be split in the gas phase, such as the splitting of n-butylalkyl ethers or n-butylaryl ethers into butene and alcohols or phenols, or the splitting of esters, vinyl ethers and alkenes with beta-positioned chlorine in the pipe reactor of Vycor glass into unsaturated chlorine compounds such as vinyl chloride. Another example is gas phase pyrolysis with benzylphenyl ether in a glass container in the presence of tetraline.
Ether splitting in the liquid phase is also possible. For instance, the pyrolysis of dibutyl ether in a gold reactor into n-butane, butyraldehyde and also 1-butanol.
For the splitting of the ethers both subcritical and supercritical solvents can also be used. For instance, thermolysis of benzylphenyl ether in subcritical and supercritical water and supercritical methanol, results in, among others, phenol and toluene.
Ethers such as 1-phenoxynaphthalene and 9-phenoxyphenanthrene are capable of being split by so-called aquathermolysis in a pipe of V4A steel only in the presence of water into 1-napthene and 9-hydroxyphenathrene and phenol respectively.
U.S. Pat. No. 6,218,580 (counterpart to EP 0 915 075), which is incorporated herein by reference, teaches that the acid-catalyzed intermolecular etherification of mono- or polyhydric alcohols and acid-catalyzed ether cleavage in the presence of water can be improved if etherification or ether cleavage is carried out in the presence of an acid catalyst with a hydrogenation catalyst under a hydrogen atmosphere. Comparison Example 2 describes cleavage of dipentaerythritol with propionic acid in water wherein the reaction mixture is heated to 280xc2x0 C.
As is known from U.S. Pat. No. 5,364,987 (counterpart to EP 0 577 972), which is incorporated herein by reference, processes for the production of 1,3-propanediol from acrolein are generally based on two reaction steps. The first step, step (a), comprises hydration of acrolein in the presence of an acid hydration catalyst. The second step, step (b), comprises catalytic hydrogenation of the reaction mixture containing 3-hydroxypropionaldehyde from step (a), which reaction mixture has been freed of unreacted acrolein. (Preferably, acrolein levels can be reduced to about 200 ppm or less.) The processes also comprises step (c), distillative refining of the reaction mixture. Pure 1,3-propanediol (which can contain as much as 99.9 weight % or more 1,3-propanediol) is obtained by distillative refining of the reaction mixture in step (c), i.e. evaporation of the water, the distillation of the residual water, intermediate boiler distillation (removing low boiling compounds) and distillation-purification.
The disadvantage of the known process for the production of 1,3-propanediol is the fact that due to various secondary reactions, especially during the hydration step, the total yield of 1,3-propanediol is reduced. During the refining of the reaction mixture from the catalytic hydrogenation, the high boiler fraction (boiling point above that of 1,3-propanediol) contains as primary products 4-oxa-1,7-heptanediol (DiPDO) (also known as 3,3xe2x80x2-oxybis-1-propanol or bis(3-hydroxypropyl)ether) and 4-hydroxy-3-hydroxymethyl tetrahydropyran (HMT, in the form of two isomers H-HMT1 and H-HMT2).
U.S. Pat. No. 5,364,987 teaches a process comprising (1) distilling the aqueous 1,3-propanediol mixture which contains by-products having boiling points higher than 1,3-propanediol; (2) separating DiPDO from the by-products having boiling points higher than 1,3-propanediol; and treating the DiPDO in aqueous solution at from 100-300xc2x0 C. with an solid acid catalyst in order to cleave DiPDO to form 1,3-propanediol; and returning the resulting reaction mixture from which the solid acid catalyst has been removed to the distilling step. U.S. Pat. No. 5,364,987 teaches that separation of DiPDO is necessary, whereas it is desired that such a separation not be used, i.e., that the high boiler sump accumulating in the process can be utilized directly.
Other processes for the producing of 1,3-propanediol can also result in the production of DiPDO and conversion of DiPDO to 1,3-propanediol would also be beneficial to these processes.
One object of this invention is to provide a simple and effective method for splitting or cleaving oligomeric water-soluble ethers.
Another objective of the present invention is to provide a method for increasing the yield of 1,3-propanediol in the process for the production of 1,3-propanediol from acrolein in a simple way.
Other objectives will become evident from the following description of the invention.
The invention is directed to a process for production of 1,3-propanediol including the steps: (a) hydrating acrolein in the presence of an acid hydration catalyst; (b) catalytically hydrogenating the reaction mixture of step (a), which reaction mixture comprises 3-hydroxypropionaldehyde and is freed of unreacted acrolein; (c) refining the reaction mixture of step (b) containing water, 1,3-propanediol and the by-products boiling higher than 1,3-propanediol; and (d) treating 4-oxa-1,7-heptanediol to form 1,3-propanediol by (1) removing a boiler sump comprising 4-oxa-1,7-heptanediol from the refining step (c), (2) treating the boiler sump in an aqueous solution in the presence of an acid catalyst at about 200 to about 300xc2x0 C. to form a solution comprising 1,3-propanediol, (3) neutralizing the solution obtained is step (2), and returning the neutralized solution from step (3) to the refining step (c).
The invention can be used to treat any such sump. According to a preferred process of making 1,3-propanediol, the sump preferably contains at least about 50 weight %, preferably at least about 55 weight %, 4-oxa-1,7-heptanediol. It preferably contains up to about 70 weight %, more preferably up to about 65 weight %, 4-oxa-1,7-heptanediol.
Preferably water is added to the boiler sump to form the aqueous solution. Preferably the water is added so that the ratio of organic compounds in the sump:water (organic:water ratio) is at least about 0.5:1, preferably at least about 1:1. Preferably, the organic:water ratio is up to about 1:20, more preferably up to about 1:8.
In one preferred embodiment, the boiler sump further comprises 4-hydroxy-3-hydroxymethyl tetrahydropyrane.
The invention is also directed to a process for splitting oligomeric water-soluble ether comprising: (a) treating an aqueous solution comprising oligomeric water-soluble ether in the presence of homogeneous acid catalyst at a temperature of from about 200 to about 300xc2x0 C. to form the monomer of the oligomeric water-soluble ether; and (b) neutralizing the solution obtained in step (a). Preferably, the oligomeric water-soluble ether is selected from the group consisting of C4-C7 ethers and mixtures thereof, more preferably the group consisting of 4-oxa-1,7-heptanediol, diethyleneglycol dimethyl ether, diglycol, dipropyleneglycol, dipropyleneglycol methyl ether, and propyleneglycol methyl ether. Preferably, the aqueous solution further comprises organic compounds having boiling points higher than the oligomeric water-soluble ether. In the most preferred embodiment, the oligomeric water-soluble ether is 4-oxa-1,7-heptanediol and the monomer is 1,3-propanediol. In that embodiment, the organic compounds having boiling points higher than the oligomeric water-soluble ether comprise 4-hydroxy-3-hydroxymethyl tetrahydropyran.
The acid catalyst is preferably a mineral acid, which is preferably selected from the group consisting of H2SO4, H3PO4 or HNO3, and mixtures thereof.
Alternatively, the acid catalyst is preferably an organic acid, which is preferably selected from the group consisting of propionic acid, trifluoracetic acid or pyridine hydrochloride, and mixtures thereof.
The acid catalyst is used in an amount of at least 0.05 weight %, more preferably at least about 0.5 weight %, based on the oligomeric ether being split, e.g., DiPDO. It is preferably used in an amount of up to 5 weight %, more preferably up to 2 weight %, based on the oligomeric ether being split.
Preferably the process is a continuous process.
The processes preferably have a selectivity of at least 50% and a yield of at least 50%.
The processes are preferably carried out in the absence of a hydrogenation catalyst.
The subject of the invention is a process for splitting or cleaving water-soluble ethers. The process comprises treating an aqueous solution of the ethers in the presence of acids at 200-300xc2x0 C. and the solution obtained neutralized.
By xe2x80x9coligomeric water-soluble etherxe2x80x9d reference is to ethers with at least two monomeric units and at least one ether bridge. As the ether, one can use C4-C7 ethers and mixtures thereof. In particular the process of the invention can be applied to the following ethers: 4-oxa-1,7-heptanediol (DiPDO); diethyleneglycol dimethyl ether (Diglyme); diglycol; dipropyleneglycol (DiPg); dipropyleneglycol methyl ether (Di PG Me); and propyleneglycol methyl ether (PG PE).
Ether splitting operations are preferably conducted in aqueous solution in the presence of homogeneous acid catalyst (that is, catalysts that are soluble in the aqueous solution in the amount used, and which are not solid catalysts), such as mineral acids and organic acids. Preferred mineral acids are H2SO4, H3PO4 or HNO3. Organic acids such as propionic acid (PrA), trifluoracetic acid (F3Cxe2x80x94COOH) or pyridine hydrochloride can also be used. Other useful homogeneous catalysts can be selected from the group consisting of Lewis Acids, Bronsted Acids, super acids, and mixtures thereof. Examples include fluorosulfonic acid, phosphorous acid, p-toluenesulfonic acid, benzenesulfonic acid, phosphotungstic acid, and trifluoromethanesulfonic acid. The most preferred catalyst is sulfuric acid.
The process should be carried out in a pipe or vessel suitable for handling the reaction, i.e., that is capable of handling hot acids. Preferred is a tantalum pipe or vessel. Steel, such as Zircolloy or Hastelloy, or glass-lined pipes or vessels can also be used.
Preferably the acid or acid catalyst is used in an amount of at least 0.05 weight %, more preferably at least about 0.5 weight %, based on the oligomeric ether being split, e.g., DiPDO. It is preferably used in an amount of up to 5 weight %, more preferably up to 2 weight %, based on the oligomeric ether being split.
The invention is also directed to a process for production of 1,3-propanediol. Hydrating acrolein in the presence of an acid hydration catalyst, and catalytically hydrogenating the reaction mixture (which comprises 3-hydroxypropionaldehyde and is substantially free of unreacted acrolein), can be carried out using known methods.
Preferably the reaction mixture comprising 3-hydroxypropionaldehyde is freed of unreacted acrolein by a separation step that occurs between steps (a) and (b). The separation can be carried out by distillation or other means of removing acrolein. A small portion of acrolein can remain after this step, but for the purpose of this invention the 3-hydroxypropionaldehyde is considered freed of unreacted acrolein. (Preferably, acrolein levels are reduced to about 200 ppm or less.)
The reaction mixture of step (b) containing water, 1,3-propanediol and the by-products boiling higher than 1,3-propanediol is refined, preferably by distillation. (The reaction mixture also contains some intermediate compounds, i.e., compound with boiling points in-between the boiling points of water and 1,3-propanediol, which are distilled off with the water.)
The 4-oxa-1,7-heptanediol that is formed during the reaction is treated to form 1,3-propanediol (PDO). Boiler sump (also called xe2x80x9cPDO sump solutionxe2x80x9d) comprising 4-oxa-1,7-heptanediol is removed from the refining step (c). Then, the sump is treated in an aqueous solution in the presence of acid at about 200 to about 300xc2x0 C. to form a solution comprising 1,3-propanediol. The invention can be used to treat any such sump. According to a preferred process of making 1,3-propanediol, the sump preferably contains at least about 50 weight %, preferably at least about 55 weight %,4-oxa-1,7-heptanediol. It preferably contains up to about 70 weight %, more preferably up to about 65 weight %, 4-oxa-1,7-heptanediol. Such a sump preferably contains hydroxy-3-hydroxymethyl tetrahydropyran (HMT) in an amount of at least about 20 weight %, more preferably at least about 25 weight %, and preferably up to about 40 weight %, more preferably up to about 35 weight %. High boiling compounds are typically present in an amount of up to 10 weight %, more preferably up to 5 weight %, probably as sludge. To form the aqueous solution water is added to the sump. Preferably the water is added so that the weight ratio of organic compounds in the sump:water (organic:water ratio) is at least about 0.5:1, preferably at least about 1:1. Preferably, the organic:water ratio is up to about 1:20, more preferably up to about 1:8. The resulting solution is neutralized. Preferably it is neutralized using calcium hydroxide, but other bases can be used (e.g., calcium carbonate, magnesium hydroxide, etc.) The base should be used in an amount suitable to remove the acid, e.g., about stoichiometric amounts. Then, the neutralized solution is returned to the refining step.
The process can be carried out using continuous or batch techniques, with continuous processes being preferred.
U.S. Pat. No. 5,364,987 (counterpart to EP 0 577 972) teaches that separation of DiPDO from the sump is necessary. An advantage of the process of the invention is the fact that the high boiler sump accumulating in the process can be utilized directly. No byproducts are formed which cannot be removed, as has been asserted.
Another advantage is that the solid catalysts described in U.S. Pat. No. 5,364,987 have a short service life. The acid used in the invention, such as mineral acid catalysts, can be removed by an ion exchanger. Ion exchangers can be regenerated. Alternatively, an insoluble salt (in the case of H2SO4) can be formed by the addition of Ca(OH)2, which is then filtered off.
The neutralized solution can be distilled together with the crude 1,3-propanediol stream of the installation without problem in the available refining without modification, i.e., it can be returned for use in step (c). No quality loss occurs.
The processes are preferably carried out in the absence of a hydrogenation catalyst, for instance, as described in U.S. Pat. No. 6,218,580, which is incorporated by reference.
High yield is achieved through high selectivity and high conversion for the desired product (e.g., 1,3-propanediol). Selectivity is preferably at least 30%, more preferably at least 40%, even more preferably at least 50%, and most preferably at least 60%. Conversion is preferably at least 30%, more preferably at least 40%, even more preferably at least 50%, and most preferably at least 60%. Desirably they are as high as 70%, 80%, 90% or more.